Functional expression of hepassocin in Escherichia coli using SUMO fusion partner and molecular chaperones

Human hepassocin (HPS) is a hepatic growth factor which can accelerate hepatocyte proliferation in vivo and protect against liver injury. Previous reports have shown that HPS expressed in Escherichia coli resulted in inclusion bodies or low yield. In this study, the application of small ubiquitin-related modifier (SUMO) fusion technology in combined with four different chaperone teams on the soluble expression of recombinant HPS protein were explored and analyzed. The soluble expression of HPS was improved significantly by SUMO fusion and co-expression with trigger factor (Tf) chaperone, which was identified by SDS-PAGE and Western blotting. The fusion protein was purified to 90% purity by metal chelate chromatography with a yield of 98 mg per liter fermentation culture. Finally, about 19 mg HPS was obtained from 1l of fermentation culture with no less than 96% purity following purification of the SUMO protease cleavage and re-purified by the Ni-NTA resin chromatography, which was the highest yield of HPS reported so far with less time and effort. The recombinant HPS significantly stimulated the proliferation of human hepatic cell line L02 cells. The present work provides an effective system for soluble expression of functional HPS, which will facilitate the clinical developments of recombinant protein drugs.